(1) Field of the Invention
This invention relates to methods for removing residual tungsten at the edge of an integrated circuit wafer after planarizing the wafer using chemical mechanical polishing, CMP, which leaves a tungsten residue at the wafer edge.
(2) Description of the Related Art
In integrated circuit fabrication it is necessary to form via holes in an inter-level dielectric material and to fill these via holes with a conductor such as tungsten. The via holes are filled by depositing a blanket layer of tungsten and then removing that part of the tungsten not in the vias using Chemical Mechanical Polishing, CMP. One of the problems encountered in this method is that the CMP does not remove the tungsten from the edge of the wafer. This residual tungsten can flake off causing contamination problems during later process steps.
U.S. Pat. No. 5,640,053 to Caldwell shows a method of removing metal from an alignment mark area.
U.S. Pat. No. 5,705,320 to Hsu et al. describes a method for recovering alignment marks after Chemical Mechanical Polishing.
U.S. Pat. No. 5,271,798 to Sandhu et al. describes a method for removing tungsten from alignment marks on a wafer.